The most widely used process for producing molten metal is based on the use of a blast furnace. Solid material is charged into the top of the furnace and molten iron is tapped from the hearth. The solid material includes iron ore (in sinter, lump or pellet form), coke, and fluxes and forms a permeable burden that moves downwardly. Preheated air, which may be oxygen enriched, is injected into the bottom of the furnace and moves upwardly through the permeable bed and generates carbon monoxide and heat by combustion of coke. The result of these reactions is to produce molten iron and slag.
A process that produces iron by reduction of iron ore below the melting point of the iron produced is generally classified as a "direct reduction process" and the product is referred to as DRI.
The FIOR (Fluid Iron Ore Reduction) process is an example of direct reduction process. The process reduces iron ore fines as the fines are gravity-fed through each reactor in a series of fluid bed reactors. The fines are reduced by compressed reducing gas that enters the bottom of the lowest reactor in the series and flows counter-current to the downward movement of fines.
Other direct reduction processes include moving shaft furnace-based processes, static shaft furnace-based processes, rotary hearth-based processes, rotary kiln-based processes, and retort-based processes.
The COREX process produces molten iron directly from coal without the blast furnace requirement of coke. The process includes 2-stage operation in which:
(a) DRI is produced in a shaft furnace from a permeable bed of iron ore (in lump or pellet form), coal and fluxes; and PA1 (b) the DRI is then charged without cooling into a connected melter gasifier. PA1 (a) forming a bath of molten iron and slag in a vessel; PA1 (b) injecting into the bath: PA1 (c) smelting the metalliferous feed material to metal in the metal layer. PA1 (a) forming a molten bath having a metal layer and a slag layer on the metal layer in a metallurgical vessel; PA1 (b) injecting a metalliferous feed material into the metal layer via one or more than one lance/tuyere and smelting the metalliferous material to metal in the metal layer; PA1 (c) injecting a solid carbonaceous material into the metal layer via one or more than one lance/tuyere in an amount that is sufficient so that the level of dissolved carbon in metal is at least 3 wt % based on the total weight of carbon and metal; PA1 (d) causing upward movement of splashes, droplets, and streams of molten material from the metal layer of the molten bath which: PA1 (e) injecting an oxygen-containing gas into the vessel via one or more than one lance/tuyere to post-combust reaction gases released from the molten bath, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath, and whereby the transition zone minimises heat loss from the vessel via the side walls in contact with the transition zone. PA1 (a) The momentum of the solid material/carrier gas causes the solid material and gas to penetrate the metal layer; PA1 (b) the carbonaceous material, typically coal, is devolatilised and thereby produces gas in the metal layer; PA1 (c) carbon predominantly dissolves into the metal and partially remains as solid; PA1 (d) the metalliferous material is smelted to metal by carbon derived from injected carbon as described above in item (c) and the smelting reaction generates carbon monoxide gas; and PA1 (e) the gases transported into the metal layer and generated via devolatilisation and smelting produce significant buoyancy uplift of molten material, namely molten metal (which includes dissolved carbon) and molten slag (which is drawn into the metal layer from above the metal layer as a consequence of solid/gas injection), and solid carbon from the metal layer which results in upward movement of splashes, droplets and streams of molten material, and these splashes, droplets, and streams entrain further slag as they move through the slag layer. PA1 (a) the above-described lances/tuyeres for injecting oxygen-containing gas and lances/tuyeres for injecting solid materials, such as metalliferous material, carbonaceous material (typically coal) and fluxes, into the vessel; PA1 (b) tap holes for discharging molten metal and slag from the vessel; and PA1 (c) one or more off-gas outlet.
Partial combustion of coal in the fluidised bed of the melter gasifier produces reducing gas for the shaft furnace.
Another known group of processes for producing molten iron is based on cyclone converters in which iron ore is melted by combustion of oxygen and reducing gas in an upper melting cyclone and is smelted in a lower smelter containing a bath of molten iron. The lower smelter generates the reducing gas of the upper melting cyclone.
A process that produces molten metal directly from ores is generally referred to as a "direct smelting process".
One known group of direct smelting processes is based on the use of electric furnaces as the major source of energy for the smelting reactions.
Another known direct smelting process, which is generally referred to as the Romelt process, is based on the use of a large volume, highly agitated slag bath as the medium for smelting top-charged metal oxides to metal and for post-combusting gaseous reaction products and transferring the heat as required to continue smelting metal oxides. The Romelt process includes injection of oxygen enriched air or oxygen into the slag via a lower row of tuyeres to provide slag agitation and injection of oxygen into the slag via an upper of tuyeres to promote post-combustion. In the Romelt process the metal layer is not an important reaction medium.
Another known group of direct smelting processes that are slag-based is generally described as "deep slag" processes. These processes, such as DIOS and AISI processes, are based on forming a deep layer of slag with 3 regions, namely: an upper region for post-combusting reaction gases with injected oxygen; a lower region for smelting metal oxides to metal; and an intermediate region which separates the upper and lower regions. As with the Romelt process, the metal layer below the slag layer is not an important reaction medium.
Another known direct smelting process which relies on a molten metal layer as a reaction medium, and is generally referred to as the HIsmelt, process, is described in International application PCT/AU96/00197 (WO 96/31627) in the name of the applicant.
The HIsmelt process as described in the International application comprises:
(i) metalliferous feed material, typically metal oxides; and PA2 (ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and PA2 (i) promotes strong mixing of metal in the slag layer of the molten bath so that the slag layer is maintained in a strongly reducing condition leading to FeO levels below 8 wt % based on the total weight of the slag in the slag layer; and PA2 (ii) extends into a space above a nominal quiescent surface of the molten bath to form a transition zone; and
The HIsmelt process also comprises post-combusting reaction gases, such as CO and H.sub.2, released from the bath in the space above the bath with oxygen-containing gas and transferring the heat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.
The HIsmelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there are ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
The HIsmelt process as described in the International application is characterised by forming the transition zone by injecting a carrier gas and metalliferous feed material and/or solid carbonaceous material and/or other solid material into the bath through a section of the side of the vessel that is in contact with the bath and/or from above the bath so that the carrier gas and the solid material penetrate the bath and cause molten metal and/or slag to be projected into the space above the surface of the bath.
The HIsmelt process as described in the International application is an improvement over earlier forms of the HIsmelt process which form the transition zone by bottom injection of gas and/or carbonaceous material into the bath which causes droplets and splashes and streams and molten metal and slag to be projected from the bath.